This invention relates to valve assemblies and particularly to such assemblies for controlling the flow of solid materials, for example powdery, particulate or granular materials, through inlets into vessels, which vessels are subsequently to be pressurised to effect conveyance of the materials therefrom and whereby the inlets thereto must be sealed during said conveyance.
It is now established practice to convey granular or powdery materials by means of pneumatic conveying equipment in which the material is fed into a despatch vessel, said vessel then being supplied with compressed air which is utilised to transport the material from the vessel along an associated pipeline to a reception hopper.
In such equipment, it is necessary to provide a control valve arrangement in the feed path to the despatch vessel which can not only interrupt the flow of material to the vessel but which, on application of the pressure to the interior of the vessel, also effectively seals said interior of the vessel.
Heretofore, the valves associated with pneumatic conveying equipment have not been totally effective in achieving these two primary objectives.
In one known type of valve assembly, the closure member comprises a blade which co-operates with a lip seal around the inlet to the vessel. The pressure within the vessel serves to deform the lip of the seal against the blade and effect the necessary seal. However, there is a strong tendency for material to be trapped between the blade and lip seal causing leakage through the seal. Further, the presence of said material, which is commonly of an extremely abrasive nature, can, together with the friction on movement of the blade over the lip seal, result in eventual wear of the lip seal whereby an effective seal cannot thereafter be achieved.
It has been proposed to overcome these problems, in particular the wear of the seal, by providing a valve assembly with a deformable seal which can be inflated into contact with an associated closure member. However such assemblies do not eliminate the possibility of material being trapped between the closure member and the seal, and are consequently such that, on inflation, the seal must first penetrate the trapped material before contact with the closure member is made.